LE BOUTEILLER, A. A. ORSTOM, leboutei@com.univ-mrs.fr
RADENAC, M. A. ORSTOM,
BLANCHOT, J. ORSTOM,
NEVEUX, J. CNRS,

 
VARIABILITY OF BIOMASS AND PRIMARY PRODUCTIVITY IN THE CENTRAL AND WESTERN EQUATORIAL PACIFIC UPWELLING
 
Two 7-8 day-long stations were occupied at the equator at 167 E in April 1988 at the onset of a La Nina event, and at 150 W in October 1994 during an El Nino period. At 167 E, a regular vertical density gradient maintained a relatively strong and steady stratification in the upper layer. Chlorophyll a showed very marked diel variations with a maximum near midday and a minimum at night. At 150 W, temperature, nutrients, chlorophyll and primary production (1.1 gC/m2/d) displayed values close to those at 167 E. However, the vertical structure of the upper layer (0 - 60 m) diurnally changed at 150 W from a nearly perfect mixed-layer at dawn to a well stratified-layer in the evening. Diel variations of chlorophyll a were also evidenced but their amplitude was much lower than at 167 E, probably due to nocturnal mixing. From estimation of the carbon content of Prochlorococcus, Synechococcus and eukaryotic cells, picophytoplankton growth rate calculation was possible at 150 W. Results showed that, in spite of lesser diel chlorophyll variations at 150 W, growth rate was high, close to one doubling per day at 10-20 m, decreasing regularly downwards.
 
Day: Thursday, Feb. 4
Time: 09:15 - 09:30am
Location: Sweeney Center
 
Code: SS39TH0915S